Comment 39 for bug 847001

Same issue on Dell Latitude E5430. Just freshly upgraded from Precise.

On Trusty:
- Using Fn+key is barely useable. Dimming by very tiny steps, and slow to react (like 10s to get OSD, 10s more to get effect).
- Using brightness settings is also slow to react (10s-ish)
- Tom Chiverton's trick works instant (i.e. echo 600 | sudo tee /sys/class/backlight/intel_backlight/brightness)

On Precise, I had some latency, but usually hammering the Fn+light key did the job just after a couple of secs.